Ion vacuum pump for magnetrons controlled for leakage of magnetron magnet



March 9, 1965 H. H. CHUN 3,173,048 ION VACUUM PUMP FOR MAGNETRONS CONTROLLED FOR LEAKAGE 0F MAGNETRON MAGNET 2 Sheets-Sheet 1 Filed March 6, 1961 Fl G. 2 INVENTOR.

HERBERT H. CHUN BY ATTORNEY March 9, 1965 H. H. CHUN ION VACUUM PUMP FOR MAGNETRONS CONTROLLED FOR LEAKAGE OF MAGNETRON MAGNET 2 Sheets-Sheet 2 Filed March 6, 1961 INVENTOR.

HERBERT H. CHUN ATTORNEY United States Patent ice The present invention relates generally to high vacuum electron discharge devices and, in particular, to novel means for extending the operational life of such devices.

Electron discharge devices envisaged in the application of the present invention include oscillator, amplifier and modulator tubes wherein an external magnetic field is an essential component and electron emission within a high vacuum envelope is the primary mechanism.

A limiting factor in the useful operational life in applicable devices has heretofore been the generation of contaminant gases occluded by the metallic structures within the vacuum chamber. Poisoning of cathodes, sputtering, power dips and numerous other phenomena have prevailed in the tube art to the present time. Removal of contaminants by vacuum pumping art during processing has advanced considerably, however, once the tube is completed and finally sealed further removal is impossible at the present state of the art.

It is, therefore, an object of the present invention to provide novel means for extending the useful life of high vacuum electron discharge devices.

The principal feature of the present invention is the removal of gaseous contaminants from the high vacuum envelope by means of externally appended getter ion vacuum pump apparatus employing the magnetic field provided as a component of the completely packaged electron discharge tube. The pump apparatus may be extremely small and is simply activated by an external DC. voltage supply.

Conventional electron discharge tubes may be restored to peak operating conditions any time after installation in equipment or during storage life when measurement of the vacuum condition indicates the presence of harmful contaminants. Tubes normally replaced after certain periods of operation may now be used for extended periods of time, limited only by the saturation level of the pump apparatus itself. As a result of increased life and maximum operating efficiency, large savings in replacement costs will also be realized with the advancement in the art taught in the present invention.

Additional objects, features and advantages will become apparent after consideration of the following detailed specification and appended drawings, in which:

FIG. 1 is a side elevation of an illustrative embodiment of the invention, namely a magnetron oscillator tube viewed from the output side;

FIG. 2 is a view of the embodiment shown in FIG. 1 rotated through 90 with a portion of the external magnet structure cut away; and

FIG. 3 is a perspective view of the illustrative embodiment of FIG. 2 rotated 180.

FIG. 4 is a cross section taken along the lines 44 of FIG. 1.

Referring now to the drawings, there is shown an embodiment of the invention of the magnetron oscillator class, having a highly evacuated envelope or tube body 1 enclosing the cathode and multi-cavity anode structure fabricated in the manner Well known in the art. External magnets 3 and 4 abut the envelope and are substantially U-shaped to provide the magnetic field essential to the operation of devices in the illustrative class. Further conventional components include an output coupling flange 3,173,048 Patented Mar. 9, 1965 2, cathode-heater tubular extension 5, cooling fins 6 and tuner assembly 7 having a driving gear 8.

In accordance with the teachings of the present invention a single cell getter ion vacuum pump apparatus 9 is externally appended and centrally located within the space defined between the parallel arms of the magnet 4. Pump 9 communicates with the interior of the tube body 1 by tribulation 12. While the pump apparatus has been shown positioned within the space defined by magnet 4, magnet 3 may be utilized similarly. In fact two or more pumps may be provided if desired.

The operation of the getteer ion vacuum pump will be briefly described to further the understanding of the invention. More detailed information is available in the literature, including Electronic Ultra High Vacuum Pump by L. D. Hall, Review Scientific Instruments, vol. 29, pp. 367-370, May 1958.

Primarily a cold cathode glow discharge is initiated and maintained between an anode16 and a plurality of cathode plates 17 with a suitable positive voltage potential applied to the anode. The cathode plates and envelope 18 are at ground potential. The pumping elements are desirably fabricated of a reactive material, such as titanium and a magnetic field of at least 1,000 gauss or more is applied perpendicular to the cathode plates. The electrons tend to flow to the anode due to the electric field and are forced into a spiral path by the presence of the strong magnetic field. The greatly increased electron path length results in a high probability of collision between free electrons and gas molecules. These collisions produce gas ions and an avalanche of free electrons. The free electrons in turn collide with other gas molecules to free ions and electrons. The positively charged gas ions then bombard the titanium cathode plates from which titanium atoms are sputtered out and deposited onto the anode. There the freshly sputtered titanium atoms combine chemically with the active gas atoms to form stable compounds. Chemically inert gas atoms are also removed by ion burial in the cathode and entrapment on the anode.

In the present invention the external magnetic circuit was calculated to provide a leakage magnetic field of 1,000-1,500 gauss in the area indicated by 15. With this field available, a single anode cell getter ion vacuum pump 9 was positioned relatively close to the cooling fins 6, since this is the point of greatest magnetic intensity. The connecting tubulation 12 was 7 inch and the pumping speed achieved with a positive D.C. voltage supply of 1,000 to 4,000 volts applied to terminal 11 of extension 10 approached .2 liter per second.

The overall packaged tube is processed through all stages including evacuation utilizing conventional vacuum pumps appropriately connected by means of tubulation 13 until a vacuum of approximately 10 Hg is measured. The tubulation is then tipped-off and sealed as at 14 to provide a complete operable tube with an appended external pump permanently incorporated. One interesting feature of the getter ion vacuum pump is the fact that pump current bears a linear relation to the density of the gas molecules within the envelope. Hence by a direct reading of pump current by means of a sensitive micro-ammeter the gaseous content of the internal atmosphere will be immediately indicated.

Since the operating efficiency of all high vacuum electron discharge devices will be hampered and life limited by the presence of gas within the envelope, the external pump may be activated to restore the original vacuum simply by connecting to a positive DC. voltage supply. Experimentation has disclosed that readings indicating a pressure of 10* or 10' mm. Hg require immediate attention to lower these values to 10- mm. Hg. or better. Pump life is another important feature since commercially available getter ion pumps utilizing titanium components have almost interminable life running into hundreds of thousands of hours.

It will be evident, therefore, that all electron discharge devices utilizing an external magnetic circuit as an essential component may be operated efficiently with the present invention over longer periods of time and shelf life need no longer present a problem to the industry. -In addition to magnetron tubese, appendage pumps may be incorporated in crossed-field tubes, amplitron, stabilitrons and others wherein sufficient space together with a leakage field "between the magnets of 1,000 gauss or better exists. 7

While a specific embodiment utilizing a one cell pump has been described, multi-cell structures may be desirable in tubes having a larger internal volume Within the tube envelope. It is intended that all matter described above or shown in the accompanying drawings be interpreted in a broad sense consonant with the spirit and scope of the invention defined in the appended claims.

What is claimed is:

1. A high vacuum electron discharge device comprising: an evacuable envelope, magnetic means mounted externally of said envelope for producing a magnetic field which threads said envelope with lines of force required for operation of said device, and a leakage field; a getter ion vacuum pump apparatus of the type adapted to produce an electrical glow discharge when energized positioned within said leakage field; and, tubulation means connecting said pump apparatus with said envelope.

2. The device according to claim 1 wherein said pump apparatus is oriented at the point of maximum leakage field intensity.

3. A high vacuum electron discharge device according to claim 1 wherein said pump apparatus comprises a cylinder with its axis aligned coaxially With the lines of force of said leakage magnetic field.

4. A high vacuum electron discharge device according to claim 1 wherein said pump apparatus comprises an internal cathode of a reactive material and an anode structure having at least one glow discharge passageway.

5. A device as claimed in claim 1 wherein said external magnetic means comprise substantially U-shaped permanent magnets with the open-ended pole pieces abutting said envelope.

References Cited by the Examiner UNITED STATES PATENTS 2,282,401 5/42 Hansell 230-69 2,507,653 5/50 Smith 313-161 X 2,726,805 12/55 Lawrence et a1. 230-69 2,755,014 7/56 Westendorp et a1. 23069 2,899,604 8/59 Dix et a1 315-3971 X 2,980,317 4/61 Reich 230-69 GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner. 

1. A HIGH VACUUM ELECTRON DISCHARGE DEVICE COMPRISING: AN EVACUABLE ENVELOPE, MAGNETIC MEANS MOUNTED EXTERNALLY OF SAID ENVELOPE FOR PRODUCING A MAGNETIC FIELD WHICH THREADS SAID ENVELOPE WITH LINES OF FORCE REQUIRED FOR OPERATION OF SAID DEVICE, AND A LEAKAGE FIELD; A GETTER ION VACUUM PUMP APPARATUS OF THE TYPE ADAPTED TO PRO- 